Electronic transmission control system with fail-safe system for automotive vehicle with continuously variable automatic transmission

Abstract

An electronic transmission control system having a fail-safe system for an automotive vehicle with a continuously variable automatic transmission whose speed-change ratio is changeable continuously depending on vehicle speed and engine load, comprises a hydraulic modulator producing at least a regulated line pressure necessary to adjust the speed-change ratio hydraulically, a desired speed-change ratio arithmetic processing section for calculating a desired speed-change ratio based on the vehicle speed and the engine load, and a desired line pressure arithmetic processing section for calculating a desired line pressure based on the desired speed-change ratio and the engine load. Also provided is a fail-safe section comprises a comparing portion for comparing the desired line pressure to a predetermined line pressure threshold above which the desired line pressure is within an unreasonably high line pressure zone, a decision portion for deciding on the basis of a result of comparison of the comparing portion whether the desired line pressure is above the predetermined line pressure threshold, and a speed-change ratio retaining portion for retaining the speed-change ratio of the continuously variable automatic transmission unchanged, when the desired line pressure exceeds the predetermined line pressure threshold.

What is claimed is: 
     
       1. An electronic transmission control system having a fail-safe system for an automotive vehicle with a continuously variable automatic transmission whose speed-change ratio is changeable continuously depending on vehicle speed and engine load, comprising: a hydraulic modulator producing at least a regulated line pressure necessary to adjust the speed-change ratio hydraulically;   a desired speed-change ratio arithmetic processing section for calculating a desired speed-change ratio based on the vehicle speed and the engine load;   a desired line pressure arithmetic processing section for calculating a first duty cycle of a line-pressure solenoid valve that corresponds to a desired line pressure based on the desired speed-change ratio and the engine load; and   a fail-safe section comprising: (a) a comparing portion for comparing the first duty cycle to a second duty cycle of the line-pressure solenoid valve that corresponds to a predetermined line pressure threshold; and   (b) a speed-change ratio retaining portion for retaining the speed-change ratio of the continuously variable automatic transmission unchanged, when the first duty cycle exceeds the second duty cycle.     
     
     
       2. The electronic transmission control system as claimed in claim 1, wherein said speed-change ratio retaining portion retains the speed-change ratio at a speed-change ratio set just before the desired line pressure exceeds the predetermined line pressure threshold. 
     
     
       3. The electronic transmission control system as claimed in claim 1, wherein the predetermined line pressure threshold is defined as a maximum value of the desired line pressure given for each of speed change ratios of the continuously variable automatic transmission. 
     
     
       4. The electronic transmission control system as claimed in claim 1, wherein the predetermined line pressure threshold is defined as a line pressure set value, providing a downshift limit preselected for each vehicle speed, so that vehicle deceleration feeling is acceptable to just below the downshift limit. 
     
     
       5. The electronic transmission control system as claimed in claim 1, wherein said hydraulic modulator has at least a duty-cycle controlled electromagnetic solenoid valve, so that the regulated line pressure is adjusted toward the desired line pressure in response to a pulsewidth modulated voltage signal of a duty cycle value, applied to the duty-cycle controlled electromagnetic solenoid valve, said desired line pressure arithmetic processing section derives the duty cycle value from the desired line pressure, and said comparing portion and said decision portion cooperate with each other to make a system-failure decision of the electronic transmission control system by comparing the duty cycle value to a predetermined duty cycle set value corresponding to a maximum value of the desired line pressure given for each of speed change ratios of the continuously variable automatic transmission. 
     
     
       6. The electronic transmission control system as claimed in claim 5, wherein said decision portion outputs a system-failure decision instruction signal of a binary number "0" when the duty cycle value is above the predetermined duty cycle set value based on the desired speed-change ratio, and said speed-change ratio retaining portion retains the speed-change ratio unchanged while the system-failure decision instruction signal of a binary number "0" is output. 
     
     
       7. The electronic transmission control system as claimed in claim 1, wherein said hydraulic modulator has at least a duty-cycle controlled electromagnetic solenoid valve, so that the regulated line pressure is adjusted toward the desired line pressure in response to a pulsewidth modulated voltage signal of a duty cycle value, applied to the duty-cycle controlled electromagnetic solenoid valve, said desired line pressure arithmetic processing section derives the duty cycle value from the desired line pressure, and said comparing portion and said decision portion cooperate with each other to make a system-failure decision of the electronic transmission control system by comparing the duty cycle value to a predetermined duty cycle set value essentially corresponding to a downshift limit that is preprogrammed for each vehicle speed, so that vehicle-deceleration feeling is acceptable to just below the downshift limit. 
     
     
       8. The electronic transmission control system as claimed in claim 7, wherein said decision portion outputs a system-failure decision instruction signal of a binary number "0" when the duty cycle value is above the predetermined duty cycle set value based on the vehicle speed, and said speed-change ratio retaining portion retains the speed-change ratio unchanged while the system-failure decision instruction signal of a binary number "0" is output. 
     
     
       9. An electronic transmission control system having a fail-safe system for an automotive vehicle with a continuously variable automatic transmission whose speed-change ratio is changeable continuously depending on vehicle speed and engine load, comprising: a line pressure control system producing a regulated line pressure;   a speed-change control system having a speed-change control valve fluidly connected to said line pressure control system for receiving the regulated line pressure and for producing a speed-change control pressure by reducing the regulated line pressure depending on a valve position of the speed-change control valve;   a link unit having a stepper motor whose angular movement is produced in response to a control command indicative of a desired speed-change ratio based on the vehicle speed and the engine load, and a linkage operable by the stepper motor and mechanically linked to the speed-change control valve, for varying the valve position of the speed-change control valve;   a desired speed-change ratio arithmetic processing section for calculating a desired speed-change ratio based on the vehicle speed and the engine load;   a desired line pressure arithmetic processing section for calculating a first duty cycle of a line-pressure solenoid valve that corresponds to a desired line pressure based on the desired speed-change ratio and the engine load; and   a fail-safe section comprising: (a) a comparing portion for comparing the first duty cycle to a second duty cycle of the line-pressure solenoid valve that corresponds to a predetermined line pressure threshold; and   (b) a speed-change ratio retaining portion for retaining the speed-change ratio of the continuously variable automatic transmission unchanged, by inhibiting the control command from being output to the stepper motor, while the first duty cycle exceeds the second duty cycle.     
     
     
       10. An electronic transmission control system having a fail-safe system for an automotive vehicle with a continuously variable automatic transmission whose speed-change ratio is changeable continuously depending on vehicle speed and engine load, comprising: a hydraulic modulating means for producing at least a regulated line pressure necessary to adjust the speed-change ratio hydraulically;   a desired speed-change ratio arithmetic processing means for calculating a desired speed-change ratio based on the vehicle speed and the engine load;   a desired line pressure arithmetic processing means for calculating a first duty cycle of a line-pressure solenoid valve that corresponds to a desired line pressure based on the desired speed-change ratio and the engine load; and   a fail-safe means comprising: (a) a comparing means for comparing the first duty cycle to a second duty cycle of the line-pressure solenoid valve that corresponds to a predetermined line pressure threshold; and   (b) a speed-change ratio retaining means for retaining the speed-change ratio of the continuously variable automatic transmission unchanged, when the first duty cycle exceeds the second duty cycle.     
     
     
       11. The electronic transmission control system as claimed in claim 10, wherein said speed-change ratio retaining means retains the speed-change ratio at a speed-change ratio set just before the desired line pressure exceeds the predetermined line pressure threshold. 
     
     
       12. The electronic transmission control system as claimed in claim 10, wherein the predetermined line pressure threshold is defined as a maximum value of the desired line pressure given for each of speed change ratios of the continuously variable automatic transmission. 
     
     
       13. The electronic transmission control system as claimed in claim 10, wherein the predetermined line pressure threshold is defined as a line pressure set value, providing a downshift limit preselected for each vehicle speed, so that vehicle deceleration feeling is acceptable to just below the downshift limit. 
     
     
       14. The electronic transmission control system as claimed in claim 10, wherein said hydraulic modulating means has at least a duty-cycle controlled electromagnetic solenoid valve, so that the regulated line pressure is adjusted toward the desired line pressure in response to a pulsewidth modulated voltage signal of a duty cycle value, applied to the duty-cycle controlled electromagnetic solenoid valve, said desired line pressure arithmetic processing means derives the duty cycle value from the desired line pressure, and said comparing means and said decision means cooperate with each other to make a system-failure decision of the electronic transmission control system by comparing the duty cycle value to a predetermined duty cycle set value corresponding to a maximum value of the desired line pressure given for each of speed change ratios of the continuously variable automatic transmission. 
     
     
       15. The electronic transmission control system as claimed in claim 5, wherein said decision means outputs a system-failure decision instruction signal of a binary number "0" when the duty cycle value is above the predetermined duty cycle set value based on the desired speed-change ratio, and said speed-change ratio retaining means retains the speed-change ratio unchanged while the system-failure decision instruction signal of a binary number "0" is output. 
     
     
       16. The electronic transmission control system as claimed in claim 10, wherein said hydraulic modulating means has at least a duty-cycle controlled electromagnetic solenoid valve, so that the regulated line pressure is adjusted toward the desired line pressure in response to a pulsewidth modulated voltage signal of a duty cycle value, applied to the duty-cycle controlled electromagnetic solenoid valve, said desired line pressure arithmetic processing means derives the duty cycle value from the desired line pressure, and said comparing means and said decision means cooperate with each other to make a system-failure decision of the electronic transmission control system by comparing the duty cycle value to a predetermined duty cycle set value essentially corresponding to a downshift limit that is preprogrammed for each vehicle speed, so that vehicle-deceleration feeling is acceptable to just below the downshift limit. 
     
     
       17. The electronic transmission control system as claimed in claim 16, wherein said decision means outputs a system-failure decision instruction signal of a binary number "0" when the duty cycle value is above the predetermined duty cycle set value based on the vehicle speed, and said speed-change ratio retaining means retains the speed-change ratio unchanged while the system-failure decision instruction signal of a binary number "0" is output. 
     
     
       18. A continuously variable automatic transmission capable of varying a speed-change ratio continuously, comprising: a speed-change ratio adjusting mechanism for producing a regulated line pressure and a speed-change control pressure necessary to adjust a speed-change ratio hydraulically; and   an electronic transmission control system comprising a data processing section performing functions;   setting a desired speed-change ratio based on vehicle speed and engine load;   outputting a control command based on the desired speed-change ratio to said speed-change ratio adjusting device;   calculating a first duty cycle of a line-pressure solenoid valve that corresponds to a desired line pressure based on the engine load and the desired speed-change ratio;   detecting whether the first duty cycle exceeds a second duty cycle of the line-pressure solenoid valve that corresponds to a predetermined line pressure threshold above which the desired line pressure is within an unreasonably high line pressure zone; and   retaining the speed-change ratio unchanged, while the first duty cycle exceeding the second duty cycle is detected.   
     
     
       19. The continuously variable automatic transmission as claimed in claim 18, wherein said speed-change ratio adjusting mechanism comprises a line pressure control system producing the regulated line pressure, a speed-change control system having a speed-change control valve fluidly connected to said line pressure control system for receiving the regulated line pressure and for producing the speed-change control pressure by reducing the regulated line pressure depending on a valve position of the speed-change control valve, and a link unit having a stepper motor whose angular movement is produced in response to the control command based on the desired speed-change ratio, and a linkage operable by the stepper motor and mechanically linked to the speed-change control valve for varying the valve position of the speed-change control valve. 
     
     
       20. The continuously variable automatic transmission as claimed in claim 19, wherein said data processing section retains the speed-change ratio unchanged by inhibiting the control command from being output to the stepper motor, while the desired line pressure exceeds the predetermined line pressure threshold. 
     
     
       21. The continuously variable automatic transmission as claimed in claim 20, wherein the predetermined line pressure threshold is defined as a maximum value of the desired line pressure given for each of speed change ratios of the continuously variable automatic transmission. 
     
     
       22. The continuously variable automatic transmission as claimed in claim 20, wherein the predetermined line pressure threshold is defined as a line pressure set value, providing a downshift limit preselected for each vehicle speed, so that vehicle deceleration feeling is acceptable to just below the downshift limit. 
     
     
       23. The continuously variable automatic transmission as claimed in claim 20, wherein said line pressure control system has at least a duty-cycle controlled electromagnetic solenoid valve, so that the regulated line pressure is adjusted toward the desired line pressure in response to a pulsewidth modulated voltage signal of a duty cycle value, applied to the duty-cycle controlled electromagnetic solenoid valve, said data processing section derives the duty cycle value from the desired line pressure, and makes a system-failure decision of the electronic transmission control system by comparing the duty cycle value to a predetermined duty cycle set value corresponding to a maximum value of the desired line pressure given for each of speed change ratios of the continuously variable automatic transmission. 
     
     
       24. The continuously variable automatic transmission as claimed in claim 23, wherein said data processing section outputs a system-failure decision instruction signal of a binary number "0" when the duty cycle value is above the predetermined duty cycle set value based on the desired speed-change ratio, and retains the speed-change ratio unchanged by inhibiting the control command from being output to the stepper motor while the system-failure decision instruction signal of a binary number "0" is output. 
     
     
       25. The continuously variable automatic transmission as claimed in claim 20, wherein said line pressure control system has at least a duty-cycle controlled electromagnetic solenoid valve, so that the regulated line pressure is adjusted toward the desired line pressure in response to a pulsewidth modulated voltage signal of a duty cycle value, applied to the duty-cycle controlled electromagnetic solenoid valve, said data processing section derives the duty cycle value from the desired line pressure, and makes a system-failure decision of the electronic transmission control system by comparing the duty cycle value to a predetermined duty cycle set value essentially corresponding to a downshift limit that is preprogrammed for each vehicle speed, so that vehicle-deceleration feeling is acceptable to just below the downshift limit. 
     
     
       26. The continuously variable automatic transmission as claimed in claim 25, wherein said data processing section outputs a system-failure decision instruction signal of a binary number "0" when the duty cycle value is above the predetermined duty cycle set value based on the vehicle speed, and retains the speed-change ratio unchanged by inhibiting the control command from being output to the stepper motor while the system-failure decision instruction signal of a binary number "0" is output.